Fuel cells are arranged in stacks for the production of commercially significant amounts of electricity. The cells are formed from plate-like constituents which are stacked one atop the other and electrically connected in series so as to produce significant voltages. In fuel cells of the type which require cooling, there will be a plurality of cooling plates interspersed throughout the stack so that the operating temperature of the entire stack will remain in a predetermined range. The specific coolant used can be gaseous or liquid. The coolant system in a power plant using one or more fuel cell stacks is generally a closed system with the coolant being circulated through the stack or stacks in heat exchange relationship with the cells to pick up heat from the latter by boiling part of the coolant.
In U.S. Pat. No. 4,678,723 issued to Wertheim on Jul. 7, 1987, a stack of fuels cells is cooled by a coolant mixture of air and entrained water droplets comprising cathode exhaust and injected water fog. The problem with the Wertheim system is that the distribution of the water and air into the multi-cell stack is nearly impossible without separating the mixture. In accordance with my invention this problem is avoided by distributing the water and the air separately into each of the coolers and mixing the air and water within the cooler.
In the prior art Parenti, Jr. et al U.S. Pat. No. 3,905,884, an electrolysis cell system includes a compact electrolysis cell comprising gas diffusion electrodes on each side of an aqueous electrolyte retaining matrix. A portion of the hydrogen gas produced by the cell has water added thereto and is recirculated through a thermal exchange portion of the cell to remove waste heat from the cell and create a temperature gradient. The amount of water sprayed into the recirculating gas stream is controlled to maintain a predetermined temperature of the gas stream emerging from the thermal exchange portion of the cell. The problem with the Parenti et al system of water boiling is that cell pressure cannot be increased without raising cell temperature, and this limits the life of the various cell material.
In the Stedman U.S. Pat. No. 3,761,316 a fuel cell assembly utilizing the waste heat of a fuel cell to provide evaporative cooling of the cell is provided by a hydrophobic separator disposed in heat conducting relationship with the fuel cell. Water is fed under pressure to a cavity on one side of the separator, and as steam evolves from the coolant, it passes through the hydrophobic separator to ambient. The present invention is an improvement over Stedman in that a carrier gas is introduced to the cooler. This allows the designer to operate the fuel cell at high pressure without raising cell temperature which limits the life of the cell materials. For example, at a cell temperature limit of 300 degrees F., the reactant pressure is limited to 67 psia. With the carrier gas concept of this invention, it is possible to operate the cell at 300 degrees F. with much higher reactant pressures of as much as 200 psia, or even greater thus enhancing performance.
Fanciullo, U.S. Pat. No. 4,098,959, Kothman U.S. Pat. No. 4,582,765 and Kamoshita U.S. Pat. No. 4,623,596 disclose structure in the form of heat exchangers located in the region of the fuel cell to be cooled. Cooling is accomplished using the latent heat of vaporization to vaporize a liquid flowing through the heat exchange structure. Taylor U.S. Pat. No. 4,706,737 discloses an inlet manifold for delivery of water to act as a coolant medium for a fuel stack.